Steam generators of pressurized-water nuclear reactors consist of a casing of great height of the order of 20 meters, the lower part of which encloses a cluster of tubes, fixed to a tubular plate, within which the pressurized water coming from the reactor vessel circulates from the bottom upwards and then from the top downwards, the tubes being bent, before it is returned to the vessel of the nuclear reactor. The supply water intended to produce the steam is introduced into the casing of the steam generator and comes in contact with the outer surface of the tubes of the cluster where it evaporates under the effect of the heat of the pressurized water circulating within the tubes of the cluster.
The upper part of the steam generator contains the water/steam separators and communicates with the circuit for processing and using the steam produced.
The tubular clusters of these steam generators comprise a very great number of tubes, for example of the order of 3000 in the case of steam generators of 900-Megawatt nuclear reactors constructed at the present time. These tubes are fixed by welding and then expanded at each of their ends onto a tubular plate of substantial thickness, one of the faces of which is in contact with the primary water which is distributed in the tubes in a compartment of a chamber consisting of two parts forming the lower end of the steam generator.
During the manufacture of the steam generator, the preparation of the holes in the tubular plate before installation of the cluster, as well as the expansion and degreasing of these tubes, are extremely long operations requiring very great care.
These operations are carried out in the workshop on the steam generator during assembly, the latter being maintained in a horizontal position on rollers allowing it to be rotated about its longitudinal axis arranged horizontally.
The cleaning of each of the holes in the tubular plate before installation of the cluster must be carried out by hand, and the work of the operators responsible for this cleaning is extremely laborious.
In the same way, the tubes have to be expanded within the tubular plate by operators using hand tools which have to be moved from one tube to the other over the entire tubular plate.
The expanding operation must be followed by an operation involving relaxing the stresses on the expanded tube at the level of the transition zone between the expanded part and the non-expanded part of the tube.
Finally, each of the tubes has to be degreased after expanding and stress removal.
There are known tools or devices which make it possible to carry out the various operations to prepare the plate and fix the cluster relatively quickly and automatically, but the movement of these tools from one hole to another in the tubular plate or from one tube to another in the cluster necessarily involves an operator, with the result that all the operations relating to a steam generator remain extremely lengthy and the manufacture of steam generators is still one of the operations which considerably slow down the manufacture of a nuclear reactor.